*{padding:0;margin:0;}
body{padding:40px 10px 0;}
.btn{position: fixed;top:4px;left:4px;z-index:1;display:block;padding:5px 10px;color: #fff;background-color: #337ab7;border:1px solid #ddd;border-color: #2e6da4;border-radius:2px;cursor:pointer;}
.btn:hover{color: #fff;background-color: #286090;border-color: #204d74;}
canvas{display: block;margin:0 auto;background-color:#fff;cursor:pointer;}